1. Field of the Invention
The present invention relates to means for correcting snaking, that is, a phenomenon in which a sensitized material or a thermosensitive paper in a roll form (hereinafter referred to as rollfilm) such as rolled film or paper is biased and shifted from a prescribed position in the width direction thereof. More specifically, it relates to a method and apparatus for correcting snaking of rollfilms in an image recording apparatus in which the rollfilm is exposed while the same is fed.
2. Description of the Prior Art
The image recording apparatuses employing rollfilms have been widely known and one example is disclosed in U.S. Pat. No. 4,080,634. The above referenced U.S. Pat. No. 4,080,634 is entitled "Halftone reproduction device with high resolution scanning and recording system", and issued to ECRM, Inc. on Mar. 21, 1978. The above referenced U.S. patent is incorporated herein by reference.
In an image recording apparatus employing rollfilms, a rollfilm is transferred, with the same nipped between a driving roller and an opposing nip roller.
On this occasion, if the shape of the roller is not a perfect right circular cylinder but is tapered, or the contact pressure of the nip roller is imbalanced in the left/right direction, then the rollfilm is not properly fed in the longitudinal direction thereof but is biased in the width direction, and the film snakes. When the rollfilm is relatively short, this snaking sometimes does present a serious problem, and may be neglected.
However, the amount of deviation is accumulated in proportion to the amount of rollfilm being fed. Therefore, when a large number of pictures are to be recorded on a long rollfilm, the snaking becomes a problem.
A number of corrective measures for snaking have been proposed. In one proposal, the pressure of the springs provided at both ends of the nip roller is adjusted so as to feed the rollfilm properly.
In another proposal, the driving roller is formed to have a convex form so that the rollfilms is automatically brought to the center of the roller.
In the first mentioned method, the pressure of the springs provided at both ends of the nip roller is adjusted to make the nip pressure level for the entire length of the roller. Therefore, the first mentioned method is troublesome and not efficient. Since an extremely delicate adjustment of the balance of the left and right nip pressure is required in the first mentioned method, there is a possibility that the pressure of the left and right nips may become imbalanced and cause snaking. Readjustment of the nip pressure is required each time this occurs.
The method includes trial and error steps in which the rollfilm is actually fed and the pressure of the nip is adjusted according to the monitored condition of snaking.
The second mentioned method employing a convex driving roller includes the step of automatically aligning the position of the rollfilm at the center of the roller. In order to accomplish this, an image reading apparatus may be employed in which the surface of the film wound around the outer circumference of the roller is subjected to slit exposure or to light beam exposure. However, such apparatus includes a problem of distortion generated in the reproduced image, since the film surface at the exposure position is warped.